Method and System for Detecting Forces on Aircraft

ABSTRACT

A system for sensing a force applied to an aircraft includes a first sensor, a second sensor, and a processor operative to define a first velocity vector as a function of a first velocity due to a rotation motion of the aircraft, define a second velocity vector as a function of a second velocity due to the rotation motion of the aircraft, define an instant axis of rotation of the aircraft as a function of the first velocity vector and the second velocity vector, determine whether a force has been exerted on a first portion of the aircraft, and output an indication that a force has been exerted on the first portion of the aircraft responsive to determining that the force has been exerted on the first portion of the aircraft.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to detecting impact forceson aircraft, and in particular to detecting landing gear impact onaircraft.

Aircraft such as, for example, rotary wing aircraft and fixed wingaircraft use a variety of sensors to provide feedback to aircraftcontrol systems. Detecting when a force, such as weight, is applied tothe landing assemblies or other portions of an aircraft provides usefulfeedback to aircraft systems. Previous systems used sensors located oneach landing assembly to determine whether weight was applied to alanding assembly. The use of these sensors increased the weight andcomplexity of the aircraft, and had limited fidelity in sensing actualweight applied to a landing assembly.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a method for sensing a forceapplied to an aircraft includes defining a first velocity vector as afunction of a first velocity due to a rotation motion of the aircraft,defining a second velocity vector as a function of a second velocity dueto the rotation motion of the aircraft, defining an instant axis ofrotation of the aircraft as a function of the first velocity vector andthe second velocity vector, determining whether a force has been exertedon a first portion of the aircraft, and outputting an indication that aforce has been exerted on the first portion of the aircraft responsiveto determining that the force has been exerted on the first portion ofthe aircraft.

According to another aspect of the invention, a system for sensing aforce applied to an aircraft includes a first sensor, a second sensor,and a processor operative to define a first velocity vector as afunction of a first velocity due to a rotation motion of the aircraft,define a second velocity vector as a function of a second velocity dueto the rotation motion of the aircraft, define an instant axis ofrotation of the aircraft as a function of the first velocity vector andthe second velocity vector, determine whether a force has been exertedon a first portion of the aircraft, and output an indication that aforce has been exerted on the first portion of the aircraft responsiveto determining that the force has been exerted on the first portion ofthe aircraft.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates a block diagram of an exemplary embodiment of anaircraft 100.

FIG. 2 illustrates an example of the geometric relationship betweensensors and a nose landing assembly of FIG. 1.

FIG. 3 illustrates a block diagram of an exemplary embodiment of logicperformed by the processor of FIG. 1.

FIG. 4 illustrates an exemplary diagram of a Euler Axis estimation.

FIG. 5 illustrates an exemplary diagram of a Euler Axis and a landingassembly.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a block diagram of an exemplary embodiment of anaircraft 100. The aircraft 100 includes a nose landing assembly 101, aleft landing assembly 103, and a right landing assembly 105. The landingassemblies may include, for example, a landing gear assembly thatincludes an inflatable wheel, or any other device that is operative tocontact a landing surface. For example a skid assembly may be used, andportions of the skid assembly may be designated as contact pointssimilar to the gear described above. The aircraft 100 includes aprocessor 102 that is communicatively connected to flight controls 104and sensors 106 that may include, for example, a gyro sensor, one ormore accelerometers, two or more velocity sensors from, for example, aglobal positioning system (GPS), or any other inertial sensors. Theprocessor 102 may also be communicatively connected to a memory 110 anda display 108.

FIG. 2 illustrates an example of the geometric relationship between asensor 106, sensor 107 and the nose landing assembly 101 including anexample of coordinate systems that are associated with the sensor 106,the sensor 107 and the nose landing assembly 101.

FIG. 3 illustrates a block diagram of an exemplary embodiment of logicperformed by the processor 102 (of FIG. 1). In this regard, theprocessor 102 receives input data from the sensors (sensors_i; wherei=1, 2, 3, . . . ) 106. The input includes acceleration (a^(i) _(x),a^(i) _(y), and a^(i) _(z)) from, for example, an accelerometer,velocity (v^(i) _(x), v^(i) _(y), v^(i) _(z)) from, for example, a GPSor derived from an accelerometer, and a rate of change in orientation(P, Q, R) from, for example, a gyro. In block 302, the processor 102performs an initialization routine that receives minimum rotationparameters (α, β, γ) 301 where α is the minimum angular velocity normthreshold value, β is the minimum angular velocity derivative normthreshold value and γ is the minimum acceleration norm threshold value,and determines whether a minimum rotation norm (MRN) condition has beensatisfied as follows:

MRN:={(|{right arrow over (ω)}|>α)&({dot over ({right arrow over(ω)}|>β}  (1)

The processor 102 resets the aircraft velocities and accelerationsvalues as follows:

$\begin{matrix}{{{{At}\text{:}\mspace{14mu} t} = {t_{1}\mspace{14mu} {where}\mspace{14mu} \left\{ {{MRN}\mspace{14mu} {is}\mspace{14mu} {true}} \right\}}},{{then}\text{:}\mspace{14mu} \left\{ \begin{matrix}{{\overset{\rightarrow}{v}}_{trans}^{i} = {{\overset{\rightarrow}{v}}^{i}\left( t_{1} \right)}} \\\& \\{{\overset{\rightarrow}{a}}_{trans}^{i} = {{\overset{\rightarrow}{a}}^{i}\left( t_{1} \right)}}\end{matrix} \right.}} & (2)\end{matrix}$

Thereafter the initialization routine outputs velocities andaccelerations due to the rotation motion of the aircraft only ({rightarrow over (v)}_(rot) ^(i) and {right arrow over (v)}_(rot) ^(i)) where:

$\begin{matrix}{{{{For}\text{:}\mspace{14mu} t} > {t_{1}\mspace{14mu} {where}\mspace{14mu} \left\{ {{MRN}\mspace{14mu} {is}\mspace{14mu} {true}} \right\}}},{{then}\text{:}\mspace{14mu} \left\{ \begin{matrix}{{\overset{\rightarrow}{v}}_{rot}^{i} = {{\overset{\rightarrow}{v}}^{i} - {\overset{\rightarrow}{v}}_{trans}^{i}}} \\\& \\{{\overset{\rightarrow}{a}}_{rot}^{i} = {{\overset{\rightarrow}{a}}^{i} - {\overset{\rightarrow}{a}}_{trans}^{i}}}\end{matrix} \right.}} & (3)\end{matrix}$

The initialization routine determines whether the acceleration norm dueto the rotation motion of the aircraft exceed the acceleration normthreshold value (γ) to output an enabling signal (Enable) to enable thelanding detection process, as follows:

if {(MRN is true) & ({right arrow over (α)}_(rot) ^(i)|>γ)}, then:Enable=1  (4)

In block 304 the processor 102 receives sensor coordinates (P^(i)_(sensor)) 303, which includes locations of the sensors, and performsEuler-Axis routine that determines an instant axis of rotation of theaircraft defined as the intersection line of two non-parallel planes asillustrated in FIG. 4. Geometrically, the intersection line, axis ofrotation, is defined by a unit directional vector {right arrow over(u)}_(axis) and a specific point defined P_(axts) on the axis. Theparametric equation of the axis of rotation is given by:

P _(axis)(s)=P _(axis) +{right arrow over (u)} _(axis) ·s  (5)

In a three dimensional space, plane A is defined by a point P and anormal vector {right arrow over (n)}. Two planes Δ¹ and Δ² are notparallel if their normal vectors {right arrow over (n)}¹ and {rightarrow over (n)}² are not parallel; this is equivalent to the crossproduct norm condition (CPN), where CPN=|{right arrow over (n)}¹×{rightarrow over (n)}²|≧μ>>0. To determine the axis of rotation directionalunit vector {right arrow over (u)}_(axis); the best two non parallelvelocity vectors are selected by maximizing CPN, where:

CPN=max{|{right arrow over (v)} _(rot) ¹ ×{right arrow over (v)} _(rot)² |,{right arrow over (v)} _(rot) ¹ ×{right arrow over (v)} _(rot) ³|,|{right arrow over (v)} _(rot) ² ×{right arrow over (v)} _(rot)³|}  (6)

In vector space, the axis of rotation directional unit vector is givenby:

$\begin{matrix}{{\overset{\rightarrow}{u}}_{axis} = \left\{ \begin{matrix}{\frac{{\overset{\rightarrow}{v\;}}_{rot}^{1} \times {\overset{\rightarrow}{v}}_{rot}^{2}}{{{\overset{\rightarrow}{v\;}}_{rot}^{1} \times {\overset{\rightarrow}{v}}_{rot}^{2}}},} & {{{if}\mspace{14mu} {CPN}} = {{{\overset{\rightarrow}{v\;}}_{rot}^{1} \times {\overset{\rightarrow}{v}}_{rot}^{2}}}} \\{\frac{{\overset{\rightarrow}{v\;}}_{rot}^{1} \times {\overset{\rightarrow}{v}}_{rot}^{3}}{{{\overset{\rightarrow}{v\;}}_{rot}^{1} \times {\overset{\rightarrow}{v}}_{rot}^{2}}},} & {{{if}\mspace{14mu} {CPN}} = {{{\overset{\rightarrow}{v\;}}_{rot}^{1} \times {\overset{\rightarrow}{v}}_{rot}^{3}}}} \\{\frac{{\overset{\rightarrow}{v\;}}_{rot}^{2} \times {\overset{\rightarrow}{v}}_{rot}^{3}}{{{\overset{\rightarrow}{v\;}}_{rot}^{2} \times {\overset{\rightarrow}{v}}_{rot}^{3}}},} & {{{if}\mspace{14mu} {CPN}} = {{{\overset{\rightarrow}{v\;}}_{rot}^{2} \times {\overset{\rightarrow}{v}}_{rot}^{3}}}}\end{matrix} \right.} & (7)\end{matrix}$

To simplify the example, CPN==|{right arrow over (v)}_(rot) ¹×{rightarrow over (v)}_(rot) ²|, thus selecting sensor_1 and sensor_2 for thedetection process.

To determine the intersection line, axis of rotation, a specific pointis found on the line, that is, to find a point P_(axis) that lies inboth planes Δ¹ and Δ², thereby solving implicit equations of Δ¹ and Δ²for P_(axis):

Δ¹ :{right arrow over (v)} _(rot) ¹·(P _(axis) −P _(sensor) ¹)=0

Δ² :{right arrow over (v)} _(rot) ²·(P _(axis) −P _(sensor) ²)=0  (8)

Equivalently solving for three coordinates P_(axis) _(—) _(x), P_(axis)_(—) _(y), and P_(axis) _(—) _(z):

$\begin{matrix}\left\{ \begin{matrix}{{{v_{{rot}\; \_ \; x}^{1}P_{{axis}\; \_ \; x}^{1}} + {v_{{rot}\; \_ \; y}^{1}P_{{axis}\; \_ \; y}^{1}} + {v_{{rot}\; \_ \; z}^{1}P_{{axis}\; \_ \; z}^{1}}} = d^{1}} \\{{{v_{{rot}\; \_ \; x}^{2}P_{{axis}\; \_ \; x}^{2}} + {v_{{rot}\; \_ \; y}^{2}P_{{axis}\; \_ \; y}^{2}} + {v_{{rot}\; \_ \; z}^{2}P_{{axis}\; \_ \; z}^{2}}} = d^{2}}\end{matrix} \right. & (9)\end{matrix}$

Where d¹ and d² are known constants given by:

$\begin{matrix}\left\{ \begin{matrix}{d^{1} = {{v_{{rot}\; \_ \; x}^{1}P_{{sensor}\; \_ \; x}^{1}} + {v_{{rot}\; \_ \; y}^{1}P_{{sensor}\; \_ \; y}^{1}} + {v_{{rot}\; \_ \; z}^{1}P_{{sensor}\; \_ \; z}^{1}}}} \\{d^{2} = {{v_{{rot}\; \_ \; x}^{2}P_{{sensor}\; \_ \; x}^{2}} + {v_{{rot}\; \_ \; y}^{2}P_{{sensor}\; \_ \; y}^{2}} + {v_{{rot}\; \_ \; z}^{2}P_{{sensor}\; \_ \; z}^{2}}}}\end{matrix} \right. & (10)\end{matrix}$

For a robust solution of Equation 9, a direct linear equation algorithmis used. First a largest absolute coordinate value, noted δ, of {rightarrow over (u)}_(axis) given by equation 7, is selected by:

δ=max{absolute(u _(axis) _(—) _(x) ,u _(axis) _(—) _(y) ,u _(axis) _(—)_(z))}  (11)

Depending of the value of 6 from equation 11, the correspondingcoordinate of P_(axis) is set to zero. Solving for the two othercoordinates, the equation 9 gives the general solution for P_(axis)expressed as:

$\begin{matrix}{P_{axis} = \left\{ \begin{matrix}{\frac{\left( {0,{{d^{2} \cdot v_{{rot}\; \_ \; z}^{1}} - {d^{1} \cdot v_{{rot}\; \_ \; z}^{2}}},{{d^{1} \cdot v_{{rot}\; \_ \; y}^{2}} - {d^{2} \cdot v_{{rot}\; \_ \; y}^{1}}}} \right)}{{v_{{rot}\; \_ \; y}^{1} \cdot v_{{rot}\; \_ \; z}^{2}} - {v_{{rot}\; \_ \; z}^{1} \cdot v_{{rot}\; \_ \; y}^{2}}};} & {{{if}\mspace{14mu} \delta} = {{abs}\left( u_{{axis}\; \_ \; x} \right)}} \\{\frac{\left( {{{d^{2} \cdot v_{{rot}\; \_ \; z}^{1}} - {d^{1} \cdot v_{{rot}\; \_ \; z}^{2}}},0,{{d^{1} \cdot v_{{rot}\; \_ \; x}^{2}} - {d^{2} \cdot v_{{rot}\; \_ \; x}^{1}}}} \right)}{{v_{{rot}\; \_ \; x}^{1} \cdot v_{{rot}\; \_ \; z}^{2}} - {v_{{rot}\; \_ \; z}^{1} \cdot v_{{rot}\; \_ \; x}^{2}}};} & {{{if}\mspace{14mu} \delta} = {{abs}\left( u_{{axis}\; \_ \; y} \right)}} \\{\frac{\left( {{{d^{2} \cdot v_{{rot}\; \_ \; y}^{1}} - {d^{2} \cdot v_{{rot}\; \_ \; y}^{2}}},{{d^{1} \cdot v_{{rot}\; \_ \; x}^{2}} - {d^{2} \cdot v_{{rot}\; \_ \; x}^{1}}},0} \right)}{{v_{{rot}\; \_ \; x}^{1} \cdot v_{{rot}\; \_ \; y}^{2}} - {v_{{rot}\; \_ \; y}^{1} \cdot v_{{rot}\; \_ \; x}^{2}}};} & {{{if}\mspace{14mu} \delta} = {{abs}\left( u_{{axis}\; \_ \; z} \right)}}\end{matrix} \right.} & (12)\end{matrix}$

In block 306, the axis-distances routine receives gear coordinates 305that include locations of the gears P^(k) _(gear) 101, 103, 105 (of FIG.1), and using equations 13 and 14, computes and outputs λ^(k)_(axis-gear) and λ_(cg) parameters defined as the distances from theestimated instant axis of rotation to the extended landing gears endpoints and the aircraft center of gravity as illustrated in FIG. 5.

λ_(axis-gear) ^(k)=|(P _(gear) ^(k) −P _(axis))×{right arrow over (u)}_(axis) |; K=1, 2, 3  (13)

λ_(cg) =|P _(axis) ×{right arrow over (u)} _(axis)|  (14)

In block 308, the detection logic determines if the distance from theaxis of rotation to a given gear is the minimum of the axis-distancesvalues and is less than a gear-axis-distance threshold value defined asa gear-cylinder-diameter λ_(cylinder) 307 and the distance from the axisof rotation to center of gravity of the aircraft exceeds thegear-axis-distance threshold value then the detection logic identifiesthe landing gear as center-of-rotation. The detection logic outputs aweight on wheel (force on wheel) signal 310 indicating contact:

$\begin{matrix}{{WoW} = {K\mspace{14mu} {if}\mspace{14mu} \left\{ \begin{matrix}{{\min\limits_{k}\left( \lambda_{{axis} - {gear}}^{k} \right)} < \lambda_{cylinder}} \\\& \\{\lambda_{cg} > \lambda_{cylinder}}\end{matrix} \right.}} & (15)\end{matrix}$

With: WOW=1→left gear; WOW=2→right gear; WOW=3→foward gear.

The gear WoW signal 310 in FIG. 3 indicates that a weight on wheel hasoccurred on the gear. The indication provides information to theaircraft 100 operator and/or automatic control systems of the aircraft100 that assists in operating the aircraft. Particularly, the weight onwheel signal may indicate that the aircraft has landed or has taken offfrom a landing area.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A method for sensing a force applied to an aircraft, the methodcomprising: defining a first velocity vector as a function of a firstvelocity due to a rotation motion of the aircraft; defining a secondvelocity vector as a function of a second velocity due to the rotationmotion of the aircraft; defining an instant axis of rotation of theaircraft as a function of the first velocity vector and the secondvelocity vector; determining whether a force has been exerted on a firstportion of the aircraft; and outputting an indication that a force hasbeen exerted on the first portion of the aircraft responsive todetermining that the force has been exerted on the first portion of theaircraft.
 2. The method of claim 1, wherein the method further includesdetermining whether a rate of change of orientation of the aircraftsatisfies a minimum rotation norm prior to defining the first and secondvelocity vectors.
 3. The method of claim 2, wherein the method furtherincludes determining whether a norm of an acceleration due to therotation motion of the aircraft is greater than a minimum accelerationnorm threshold value responsive to determining whether the rate ofchange of orientation of the aircraft satisfies the minimum rotationnorm.
 4. The method of claim 1, wherein the method further includesreceiving a first signal from a first sensor indicative of a velocity ofthe aircraft, an acceleration of the aircraft, and a rate of change oforientation of the aircraft.
 5. The method of claim 1, wherein the firstvelocity vector is associated with a first sensor, and the secondvelocity vector is associated with a second sensor.
 6. The method ofclaim 5, wherein the instant axis of rotation of the aircraft is furtherdefined as a function of a position of the first sensor and a positionof the second sensor.
 7. The method of claim 1, wherein the defining theinstant axis of rotation includes defining the instant axis of rotationas a line of intersection between a first plane perpendicular to thefirst velocity vector and a second plane perpendicular to the secondvelocity vector, wherein the first plane is not parallel to the secondplane.
 8. The method of claim 1, wherein the determining whether a forcehas been exerted on a portion of the aircraft includes: calculating adistance between the first portion of the aircraft and the instant axisof rotation; calculating a distance between a center of gravity of theaircraft and the instant axis of rotation; determining whether thedistance between the first portion of the aircraft and the instant axisof rotation is a minimum of an set of axis of rotation distance values,and whether the distance between the portion of the aircraft and theinstant axis of rotation is less than a gear-axis-distance thresholdvalue; and determining whether the distance between a center of gravityof the aircraft and the instant axis of rotation exceeds thegear-axis-distance threshold value.
 9. The method of claim 1, whereinthe force applied to the first portion of the aircraft is a weight onwheel force.
 10. The method of claim 1, wherein the first portion of theaircraft includes a landing gear assembly.
 11. A system for sensing aforce applied to an aircraft comprising: a first sensor; a secondsensor; and a processor operative to define a first velocity vector as afunction of a first velocity due to a rotation motion of the aircraft,define a second velocity vector as a function of a second velocity dueto the rotation motion of the aircraft, define an instant axis ofrotation of the aircraft as a function of the first velocity vector andthe second velocity vector, determine whether a force has been exertedon a first portion of the aircraft, and output an indication that aforce has been exerted on the first portion of the aircraft responsiveto determining that the force has been exerted on the first portion ofthe aircraft.
 12. The system of claim 11, wherein the processor isfurther operative to determine whether a rate of change of orientationof the aircraft satisfies a minimum rotation norm prior to defining thefirst and second velocity vectors.
 13. The system of claim 12, whereinthe processor is further operative to determine whether a norm of anacceleration due to the rotation motion of the aircraft is greater thana minimum acceleration norm threshold value responsive to determiningwhether the rate of change of orientation of the aircraft satisfies theminimum rotation norm.
 14. The system of claim 11, wherein the processoris further operative to receive a first signal from the first sensorindicative of a velocity of the aircraft, an acceleration of theaircraft, and a rate of change of orientation of the aircraft.
 15. Thesystem of claim 11, wherein the first velocity vector is associated witha first sensor, and the second velocity vector is associated with asecond sensor.
 16. The system of claim 15, wherein the instant axis ofrotation of the aircraft is further defined as a function of a positionof the first sensor and a position of the second sensor.
 17. The systemof claim 11, wherein the defining the instant axis of rotation includesdefining the instant axis of rotation as a line of intersection betweena first plane perpendicular to the first velocity vector and a secondplane perpendicular to the second velocity vector, wherein the firstplane is not parallel to the second plane.
 18. The system of claim 11,wherein the determining whether a force has been exerted on a portion ofthe aircraft includes: calculating a distance between the first portionof the aircraft and the instant axis of rotation; calculating a distancebetween a center of gravity of the aircraft and the instant axis ofrotation; determining whether the distance between the first portion ofthe aircraft and the instant axis of rotation is a minimum of a set ofaxis of rotation distance values, and whether the distance between theportion of the aircraft and the instant axis of rotation is less than agear-axis-distance threshold value; and determining whether the distancebetween a center of gravity of the aircraft and the instant axis ofrotation exceeds the gear-axis-distance threshold value.
 19. The systemof claim 11, wherein the force applied to the first portion of theaircraft is a weight on wheel force.
 20. The system of claim 11, whereinthe first portion of the aircraft includes a landing gear assembly.